Novel Quaternary Lanthanum Bismuth Sulfides Pb₂La_xBi_8-xS₁₄, Sr₂La_xBi_8-xS₁₄, and Cs₂La_xBi_10-xS₁₆ with Complex Structures

Abstract

The compounds Pb(2)La(x)Bi(8-x)S(14) (I), Sr(2)La(x)Bi(8-x)S(14) (II), and Cs(2)La(x)Bi(10-x)S(16) (III) were synthesized from the corresponding elements or binary sulfides at temperatures above 850 degrees C. Compounds I and II are isostructural, forming a new structure type, while the structure of III is related to the structure of the mineral kobellite. All compounds crystallize in the orthorhombic space group Pnma (No. 62) with a = 21.2592(4) A, b = 4.0418(1) A, c = 28.1718(3) A, Z = 4 for I, a = 21.190(1) A, b = 4.0417(2) A, c = 28.285(2) A, Z = 4 for II and a = 34.893(4) A, b = 4.0697(4) A, c = 21.508(2) A, Z = 4 for III. All compounds exhibit mixed site occupancy between Bi and La. Furthermore, I and II exhibit disorder between the divalent atom (Sr or Pb) and/or La and/or Bi. The structures of I and II consist of thin walls made of two metal-atom-thick NaCl-type blocks running in two opposite directions in the ac plane, forming rhombus-shaped tunnels. These tunnels are filled with Bi(2)Te(3)-type fragments. In the points where the walls intersect they form Gd(2)S(3)-type fragments. The structure of III consists of a complex three-dimensional framework with Cs-filled tunnels. All compounds are semiconductors with band gaps around 1.0 eV, and they melt around 740-860 degrees C.

The Two-Dimensional AxCdxBi4–xQ6 (A = K, Rb, Cs; Q = S, Se): Direct Bandgap Semiconductors and Ion-Exchange Materials

“…The coordination geometries are generally distorted such as capped octahedra, capped trigonal prisms, or trigonal bipyramids . Often, when other atoms are present the Bi 3+ atom sites can be occupied with similarly sized atoms, such as Pb, Sn, lanthanides, alkali metals, or alkaline earth metals thereby exhibiting mixed occupancy. ,,, The Bi-Q octahedra in these structures generally form large blocks which can be conceptually thought to derive from the NaCl-, Bi 2 Te 3 -, CdI 2 -, and Sb 2 Se 3 -type structures. , …”

Homologous Series of 2D Chalcogenides Cs–Ag–Bi–Q (Q = S, Se) with Ion-Exchange Properties

“…Bismuth chalcogenide compounds are a special class because they exhibit amazingly diverse compositions and structures. , The trivalent Bi atoms in the structures can have coordination numbers varying from 3 to 9, and the inert 6s lone pair of electrons defines the electronic character of the compounds. In these compounds the BiQ 6 (Q = S, Se, Te) octahedra can combine by edge or face sharing to form blocks or modules that are fragments excised from the NaCl-, Bi 2 Te 3 -, CdI 2 -, and Sb 2 Se 3 -type structures. ,,, Furthermore, Bi atoms can share sites with similar sized cations, such as alkali or alkaline earth metals, Cu + , Pb 2+ , Sn 2+ , Ag + , Cd 2+ or lanthanides. − Ternary or quaternary alkali metal chalcogenides A/M/Bi/Q (A = Li, K, Rb, Cs; M = Sn, Pb, Ag, Cd; Q = S, Se Te) form readily and tend to possess tunneled or layered structures. For example, the A m [M 1+ l Se 2+ l ] 2 m [M 1+2 l + n Se 3+3 l + n ] (A = alkali metal, M = Sn and Bi) homologous superseries ,, features compounds with tunneled structures, while the members of the Cs 4 [Bi 2 n +4 Te 3 n +6 ], CsM m Bi 3 Te 5+ m , , [MTe] n [Bi 2 Te 3 ] m (M = Ge, Sn, Pb) − and A 2 [M 5+ n Se 9+ n ] (A = Rb, Cs; M = Bi, Ag, Cd) series possess layered structures.…”

PbMnIn2S5: Synthesis, Structure, and Properties

“…The Pb cation is 8-fold-coordinated in a bicapped trigonal prism with Pb–S distances of 3.182(2), 2.755(3), and 3.307(3) Å (Figure S1 in the SI and Table ). This coordination feature is commonly observed in other related lead chalcogenides. − ,,− Also, distortion of the PbS 8 polyhedron may be related to the stereochemistry activity of Pb 2+ electrons as seen in other examples, such as Pb 5.5 Fe 1.5 In 10 S 22 , Pb 8.04 Fe 0.47 In 17.37 Se 34 , and Pb 8 MIn 17 S 34 (M = Cu, Ag, Au) …”